1. Field of the Invention
The present invention relates to magnetic heads and, more particularly, is directed to a magnetic head of a parallel gap configuration called a metal-in-gap type magnetic head suitable for recording and reproducing a signal on a magnetic recording medium with a high coercive force in which magnetic core halves are opposed through magnetic metal thin films of a high permeability between which a magnetic gap is sandwiched so that the halves are opposed to the magnetic gap in parallel thereto.
2. Description of the Prior Art
Recently, a wavelength of an information signal recorded by a magnetic recording/reproducing apparatus such as a video tape recorder (VTR) has become shorter so as to improve quality of an image to be recorded. Accordingly, there has been employed a recording medium with a high coercive force such as a metal tape formed by using ferromagnetic metal powder as magnetic powder or an evaporated tape which is formed by directly depositing ferromagnetic metal material on a base film or the like. The metal-in-gap type magnetic head whose magnetic gap of a magnetic core is formed by magnetic metal thin films has been proposed as a magnetic head suitable for use for the magnetic recording medium with a high coercive force.
An example of the conventional metal-in-gap type magnetic heads will be explained with reference to FIG. 1. As shown in FIG. 1, two magnetic core halves 11 and 12 which are fabricated separately are abutted through a magnetic gap g and then integrally combined to thereby form a magnetic head.
In the magnetic core halves 11 and 12, core portions are formed by magnetic oxide material portions 1 and 2 made of a material such as a single crystal ferrite or the like, respectively. The magnetic oxide material portions 1 and 2 are deposited, with magnetic metal thin films 3 and 4 made of a material such as FeAlSi alloy, FeGaSiRu alloy or the like having a high saturation magnetic flux density, on opposite surfaces thereof each extending from a front side forming an opposing surface 7 opposing to a magnetic recording medium to a back side 17 thereof.
The thus prepared magnetic core halves 11 and 12 are opposed such that the magnetic metal thin films 3 and 4 thereof are opposed each other and then abutted through a gap spacer (not shown) to thereby form the magnetic gap g therebetween. Track width defining or confining grooves 9 are formed at both sides of the magnetic gap g, for example, so that the grooves 9 define a track width Tw of the magnetic gap g.
The track width defining grooves 9 are formed in the magnetic oxide material portions 1 and 2 so as to communicate from the front side, that is, the opposing surface 7 to the back side 17. Fusing glass 8 fused in a fusion furnace or the like is filled in the grooves 9 to thereby couple the magnetic core halves 11 and 12.
Then, a coil is wound in a winding groove 5 provided at an intermediate portion between a front portion and a back portion of each of the magnetic oxide material portions 1 and 2. Thus, the magnetic core halves 11 and 12 are opposed through the magnetic metal thin films 3 and 4 with high permeability between which the magnetic gap g is sandwiched so that the halves 11 and 12 are opposed to the magnetic gap g in parallel thereto. Namely, abutment surfaces of the magnetic metal thin films 3 and 4, that is, a gap surface 10 is provided in parallel to interfaces 1S and 2S between the magnetic metal thin films 3, 4 and the magnetic oxide material portions 1, 2 at the front portion, thereby a ring type magnetic head of a parallel gap configuration is provided.
According to the thus constituted conventional magnetic head, portions extending substantially vertically to the gap surface 10, that is, vertical surfaces 5a are provided at parts of the track width defining grooves 9 and the winding grooves 5. Thus, in a case of forming the magnetic metal thin films 3 and 4 on these grooves 5 and 9 by the deposition, the sputtering process or the like, these thin films are not sufficiently grown on the vertical surfaces 5a since molecules or particles of the film material are prevented from flowing or being impinged on the vertical surfaces due to upper edge portions of the vertical surfaces 5a. Further, columnar crystal structure of the thus formed thin films becomes rough and so density of the thin films substantially vary on the vertical surfaces, so that the thin films may be formed as insufficient films. Furthermore, a thickness of the thin films only on the vertical surfaces 5 may be less than a half of those of other portions thereof and so on. Accordingly, it has been difficult to form the magnetic metal thin films 3 and 4 on all the inner surfaces of the grooves 5 and 9 with uniform and good film characteristics such as a high permeability and a low coercive force.
Thus, in the thus constituted magnetic head, magnetic fluxes generated in a recording or a reproducing mode can not flow through the magnetic metal thin films 3 and 4 on the vertical surfaces 5a but flow in the magnetic oxide material portions 1 and 2 at the area on the vertical surfaces 5a then flow in the magnetic metal thin films 3 and 4 at the area on other surfaces of the grooves. Therefore, even if the magnetic metal thin films 3 and 4 with a high permeability are deposited, the magnetic metal thin films 3 and 4 can not make an entire permeability thereof larger than that of the magnetic oxide material portions 1 and 2 but can improve only the saturation magnetic flux density, so that the thus constituted conventional magnetic head of the parallel gap configuration has the disadvantage that the electromagnetic-conversion characteristic thereof can not be improved.
Further, as a magnetic head of the metal-in-gap structure in which a magnetic metal thin film with a high permeability constitutes a main path for magnetic fluxes, there has been proposed a magnetic head called a laminated type magnetic head in which the magnetic metal thin films are laminated so that each film is sandwiched by guard material such as magnetic ferrite in a track width direction. The laminated type magnetic head has the disadvantages such that productivity of the head may be degraded since manufacturing processes thereof are relatively long and that defects are likely produced at a high rate in manufacturing procedure thereof to thereby degrade yield.
Further, since the magnetic metal thin film utilized in the metal-in-gap type head is required to have a thickness substantially same as the track width, the formation of the thin film is very difficult when manufacturing a head with a relatively large track width since the conventional magnetic head of the parallel gap type has the vertical surfaces 5a.